Not applicable.
This invention relates to preparation of what at least initially are aqueous solutions of nickel salts. It is known that in thermodynamic principle such solutions can be prepared by dissolving metallic nickel in aqueous solutions of acids, but it is also known that in practice such reactions are often impractically slow in most non-oxidizing acids and even in some oxidizing acids under certain conditions, under which the phenomenon known as xe2x80x9cpassivityxe2x80x9d occurs.
Nickel cations dissolved in water (along with some counterions) are an important constituent of many of the important types of liquid metal surface treatment chemical compositions that are known as xe2x80x9cconversion coating solutionsxe2x80x9d or a like term and are fundamentally characterized by their ability to react with surfaces of many corrosion prone metals to form on the metal surfaces a solid coating layer that includes anions from the conversion coating solution and at least some cations derived from the metal coated and that improves the corrosion resistance and/or lubricant carrying capacity of the surface so coated.
Dissolved nickel cations could of course be supplied to aqueous solutions desired to contain them by dissolving a water soluble nickel salt. However, all such salts that are readily available at an economically reasonable price are hydrated and are susceptible to various degrees of hydration dependent on the conditions under which they are stored. It is therefore difficult under large-scale manufacturing conditions to obtain reliable amounts of nickel from these salts without the inconvenience and expense of frequent chemical analysis to quantify their nickel content. Aqueous solutions with known and consistent concentrations of nickel cations are accordingly preferred, and a major object of this invention is to provide such solutions at an economically acceptable cost.
Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word xe2x80x9caboutxe2x80x9d in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, throughout the description, unless expressly stated to the contrary: percent, xe2x80x9cparts ofxe2x80x9d, and ratio values are by weight or mass; the term xe2x80x9cpolymerxe2x80x9d includes xe2x80x9coligomerxe2x80x9d, xe2x80x9ccopolymerxe2x80x9d, xe2x80x9cterpolymerxe2x80x9d and the like; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description or of generation in situ within the composition by chemical reaction(s) noted in the specification between one or more newly added constituents and one or more constituents already present in the composition when the other constituents are added, and does not preclude unspecified chemical interactions among the constituents of a mixture once mixed; specification of constituents in ionic form additionally implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole and for any substance added to the composition; any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to an object of the invention; the word xe2x80x9cmolexe2x80x9d means xe2x80x9cgram molexe2x80x9d, and the word itself and all of its grammatical variations may be used for any chemical species defined by all of the types and numbers of atoms present in it, irrespective of whether the species is ionic, neutral, unstable, hypothetical, or in fact a stable neutral substance with well defined molecules; and the terms xe2x80x9csolutionxe2x80x9d, xe2x80x9csolublexe2x80x9d, xe2x80x9chomogeneousxe2x80x9d, and the like are to be understood as including not only true equilibrium solutions or homogeneity but also dispersions that show no visually detectable tendency toward phase separation over a period of observation of at least 100, or preferably at least 1000, hours during which the material is mechanically undisturbed and the temperature of the material is maintained within the range of 18-25xc2x0 C.
It has been found that:
if metallic nickel is in large pieces, it will dissolve within a few hours in non-oxidizing acid aqueous solutions only if an oxidizing agent that is chemically different from the non-oxidizing acid is present in the non-oxidizing acid aqueous solutions in a substantial concentration;
if metallic nickel is in sufficiently finely divided powder form, most of the nickel will dissolve within a few hours in a non-oxidizing aqueous acidic solution that does not contain any separate oxidizing agent; much of any residual material will then dissolve within a few more hours if oxidizing agent is added to the aqueous acid solution in contact with the still-undissolved residue from the nickel powder;
metallic nickel derived from decomposition of nickel carbonyl is sufficiently pure to be satisfactory as a source of nickel cation solutions for conversion coating;
either large or small particles of nickel derived from decomposition of nickel carbonyl leave some insoluble residue when dissolved in aqueous non-oxidizing acid solutions, but when this residue is separated by filtration, the resulting solutions are satisfactory sources of nickel cations for high quality conversion coating solutions.
Accordingly, a process according to the invention comprises, preferably consists essentially of, or more preferably consists of, at least the following operations:
(I) providing a first mass of a solid, predominantly elemental nickel reagent;
(II) providing, separately from said first mass, a second mass of a precursor aqueous acidic liquid reagent that comprises, preferably consists essentially of, or more preferably consists of the following components:
(A) water;
(B) molecules of at least one non-oxidizing acid; and, optionally, one or both of the following components:
(C) an oxidizing agent component that contains molecules of at least one oxidizing agent that is distinct from said non-oxidizing acid; and
(D) dissolved nickel cations; and
(III) effecting contact between said first mass and said second mass under such conditions of temperature and relative motion between said two masses as will result in spontaneous chemical reaction between them, said spontaneous chemical reaction converting at least, with increasing preference in the order given, 80, 90, 95, or 98 percent of the elemental nickel present in said first mass to dissolved nickel cations in a final aqueous acidic liquid that includes some of the molecules of non-oxidizing acid originally present in said second mass within a time interval, beginning with the first contact between said first and second masses, that is not more than, with increasing preference in the order given, 24, 20, 16, 12, or 10 hours.
Suitable and preferred non-oxidizing acids for use in a process according to this invention are formic, acetic, sulfuric, hydrochloric, hydrobromic, hydriodic, hydrofluoric, phosphorous and condensed phosphorous, and phosphoric and condensed phosphoric acids. At least for economy when preparing phosphate conversion coating solutions, orthophosphoric acid is most preferred.
The solid, predominantly nickel reagent (hereinafter usually more briefly described as xe2x80x9cnickeliferous solidxe2x80x9d) used as a starting material in a process according to the invention preferably contains at least, with increasing preference in the order given, 98.0, 99.0, 99.2, 99.4, or 99.6 percent by weight of nickel and independently contains minimal amounts, as specified in detail below, of the following elements, with preferences being independent for each element:
not more than, with increasing preference in the order given, 10,000, 5000, 3000, 2500, 2000, 1500, 1250, 1000, or 750 parts of oxygen per million parts by weight of the starting nickeliferous solid, this unit of concentration being hereinafter freely applied to any other constituent of any composition and being hereinafter usually abbreviated as xe2x80x9cppmxe2x80x9d;
not more than, with increasing preference in the order given, 7500, 5000, 3000, 2500, 2000, 1500, 1250, 1000, 800, 700, or 650 ppm of carbon;
not more than, with increasing preference in the order given, 100, 80, 60, 50, 40, 30, 25, 19, 14, or 9 ppm of nitrogen;
not more than, with increasing preference in the order given, 50, 40, 30, 20, 15, 10, 8, 6, or 4 ppm of iron;
not more than, with increasing preference in the order given, 25, 20, 15, 10, 8, 6, 4, or 2 ppm of either of silicon and sodium;
not more than, with increasing preference in the order given, 15, 12, 10, 8, 6, 4, 2, or 1.0 ppm of any of boron, calcium, magnesium, and sulfur;
not more than, with increasing preference in the order given, 7, 5, 3, 2.0, 1.5, 1.0, 0.8, or 0.6 ppm of any of copper, gallium, and zinc;
not more than, with increasing preference in the order given, 3.0, 2.0, 1.5, 1.0, 0.8, 0.6, 0.4, or 0.2 ppm of any of aluminum, bismuth, cobalt, indium, lead, selenium, and thallium;
not more than, with increasing preference in the order given, 1.5, 1.0, 0.8, 0.6, 0.40, 0.30, 0.27, 0.24, 0.21, 0.18, 0.15, or 0.12 ppm of any of silver, arsenic, barium, beryllium, cadmium, chromium, manganese, molybdenum, phosphorus, antimony, tin, tellurium, titanium, or vanadium.
Nickel objects of any size can be used in a process according to the invention if sufficient oxidizing agent is supplied along with the nickel and acid used for dissolution. However, to minimize the consumption of oxidizing agent as is usually desired, the nickel used preferably is in the form of fine powder. More particularly, the volume percent of the powder retained or passed by channels of various diameters preferably conforms to the following conditions, independently for each but more preferably for any two or more of them, with greater preference the greater the number of the following conditions satisfied:
the volume percent retained by channels of 248 micrometers, (hereinafter usually abbreviated as xe2x80x9cxcexcmxe2x80x9d) is not more than, with increasing preference in the order given, 10, 5, 2.0, 1.0, 0.5, 0.2, 0.10, 0.05, 0.02, 0.005, 0.002, or 0.0005;
the volume percent passed by channels of 248 xcexcm and retained by channels of 176 xcexcm is not more than, with increasing preference in the order given, 10, 5, 4.0, 3.5, 3.0, 2.5, or 2.0;
the volume percent passed by channels of 176 xcexcm and retained by channels of 124 xcexcm is not more than, with increasing preference in the order given, 20, 15, 10, 9.0, 8.0, 7.0, 6.0, or 5.5;
the volume percent passed by channels of 124 xcexcm and retained by channels of 88 xcexcm is not more than, with increasing preference in the order given, 30, 25, 20, 15, 10, 9.0, 8.5, or 8.0;
the volume percent passed by channels of 88 xcexcm and retained by channels of 62 xcexcm is not more than, with increasing preference in the order given, 30, 25, 20, 15, 12, 10, or 9.0;
the volume percent passed by channels of 62 xcexcm and retained by channels of 44 xcexcm is not more than, with increasing preference in the order given, 50, 40, 30, 25, 20, 18, 16, 14, 12, or 10;
the volume percent passed by channels of 44 xcexcm and retained by channels of 31 xcexcm is not more than, with increasing preference in the order given, 50, 40, 30, 25, 20, 18, 16, 14, 13.0, 12.0, or 11.0;
the volume percent passed by channels of 31 xcexcm and retained by channels of 22 xcexcm is not more than, with increasing preference in the order given, 50, 40, 30, 25, 20, 18.0, 17.0, 16.0, 15.0, 14.0, or 13.0;
the volume percent passed by channels of 22 xcexcm and retained by channels of 15.6 xcexcm is not more than, with increasing preference in the order given, 50, 40, 30, 25, 20, or 18 and independently preferably is not less than, with increasing preference in the order given, 4, 6, 8, 10, or 12;
the volume percent passed by channels of 15.6 xcexcm and retained by channels of 11.0 xcexcm is not more than, with increasing preference in the order given, 50, 40, 30, 25, 21, or 19 and independently preferably is not less than, with increasing preference in the order given, 4, 6, 8, 10, or 11.5;
the volume percent passed by channels of 11.0 xcexcm and retained by channels of 7.8 xcexcm is not more than, with increasing preference in the order given, 50, 40, 30, 25, 21, 19 or 17 and independently preferably is not less than, with increasing preference in the order given, 2, 4, 6, 7.0, 8.5, 9.0, 9.4, or 9.7;
the volume percent passed by channels of 7.8 xcexcm and retained by channels of 5.5 xcexcm is not more than, with increasing preference in the order given, 30, 25, 22, 19, or 17 and independently preferably is not less than, with increasing preference in the order given, 2, 4, 5.0, 5.5, 6.0, 6.5, 7.0, or 7.3;
the volume percent passed by channels of 5.5 xcexcm and retained by channels of 3.9 xcexcm is not more than, with increasing preference in the order given, 30, 25, 22, 19, 16, 13, 10, 8.5, or 7.2;
the volume percent passed by channels of 3.9 xcexcm and retained by channels of 1.9 xcexcm is not more than, with increasing preference in the order given, 20, 15, 10, 8, 6.0, 5.0, 4.0, 3.5, or 3.0; and
the volume percent not retained by channels of 1.9 xcexcm is not more than, with increasing preference in the order given, 2.0, 1.0, 0.5, 0.2, 0.10, 0.05, 0.02, 0.005, 0.002, or 0.0005.
(It should be noted that the sizes of the xe2x80x9cchannelsxe2x80x9d as cited in the paragraphs immediately next above are part of a standardized test method generally used by suppliers of nickel powder. There is no intended implication that the channel sizes correspond precisely to particle sizes that might be measured by other methods, such as micrographic analysis of individual particles. On the contrary, it is widely believed that the sizing of particles by passage through these channels gives larger size values than would be found in a hypothetical xe2x80x9cperfectxe2x80x9d method of particle size analysis, because of the possibilities of agglomerations of particles that are not broken up by their passage through the test channels, variations in the orientation of non-equiaxed particles with respect to the direction of passage through the channels, and the like. These over-estimates of size can be quite substantial. For example, a powder specified by its supplier to have an average size of about 50 xcexcm, using the channel passage method, produces scanning electron micrographs in which most of the particles appear to be about 8 xcexcm in size.)
When an oxidizing agent is used, it is preferably one that does not result in the addition of extraneous substances to the solution of nickel salt eventually prepared in a process according to the invention. Ozone and hydrogen peroxide both satisfy this preference, because the only residues from them after they function as oxidizing agents are water and gaseous oxygen, which is of course present in any liquid exposed to the natural atmosphere. Because it is far more conveniently available than any other known oxidizing agent that is free from extraneous residues, hydrogen peroxide is most preferred.
The quantity of hydrogen peroxide preferred and its preferred time of use depend on the size of the pieces and/or particles of nickeliferous solid materials used as the primary source of nickel in a process according to the invention. If any part of the nickeliferous solid that is reacted consists of pieces each longer in any dimension than 0.5 millimeter (this unit, in either singular or plural, being hereinafter usually abbreviated as xe2x80x9cmmxe2x80x9d), the hydrogen peroxide preferably is present from the beginning of reaction in the aqueous acidic solution reacted with the nickeliferous solid, and the amount of hydrogen peroxide so present depends only on the amount of nickeliferous solid reacted that does consist of pieces each longer in any dimension than 0.5 mm, nickeliferous solid that is in pieces of this size being hereinafter denoted as xe2x80x9cnon-powderyxe2x80x9d. The number of moles of hydrogen peroxide present from the beginning of reaction preferably has a ratio to the number of moles of non-powdery nickeliferous solid reacted that is at least, with increasing preference in the order given, 0.10:1.00, 0.20:1.00, 0.30:1.00, 0.40:1.00, 0.50:1.00, 0.60:1.00, 0.70:1.00, 0.80:1.00, 0.90:1.00, 1.00:1.00, or 1.1:1.00 and independently preferably, at least for economy, is not more than, with increasing preference in the order given, 3.0:1.00, 2.5:1.00, 2.2:1.00, 2.0:1.00, 1.8:1.00, 1.6:1.00, 1.5:1.00, 1.4:1.00, or 1.3:1.00.
In contrast, if at least, with increasing preference in the order given, 95, 97, or 99 percent of the nickeliferous solid reacted passes through channels with a diameter of at least, with increasing preference in the order given, 0.40, 0.30, or 0.25 millimeter, then no oxidizing agent at all is necessary in a process according to the invention. If hydrogen peroxide or another oxidizing agent is nevertheless used, as is generally preferred in order to convert as much as possible of the nickel in the nickeliferous solid to one or more dissolved nickel salts, the addition of oxidizing agent is preferably delayed until at least, with increasing preference in the order given, 75, 85, 95, or 97% of the mass of the nickeliferous solid brought into contact with acid in a process according to the invention has already dissolved, and the amount of oxidizing agent then added preferably is based on the amount of nickeliferous solid that remains undissolved. More particularly, the number of moles of hydrogen peroxide added preferably has a ratio to the number of moles of nickeliferous solid remaining undissolved, the number of moles of the nickeliferous solid being calculated for this purpose by assuming that the nickeliferous solid is pure nickel, that is at least, with increasing preference in the order given, 0.2:1.00, 0.4:1.00, 0.6:1.00, 0.80:1.00, 0.90:1.00, 0.95:1.00, 1.00:1.00, 1.05:1.00, or 1.10:1.00 and independently preferably, at least for economy, is not more than, with increasing preference in the order given, 10:1.00, 8:1.00, 6:1.00, 4:1.00, 2.0:1.00, 1.5:1.00, or 1.3:1.00. Oxidant may alternatively be added at any earlier stage even when all or substantially all of the nickeliferous solid consists of fine particles, but any such oxidant usually does not increase the reaction rate enough to justify the cost of the added oxidant.
If all or part of the oxidizing agent selected is not hydrogen peroxide, the number of moles stated in these immediately preceding preferences should be adjusted as needed, based on the number of electrons per molecule acquired by the other oxidizing agent(s) during its/their expected oxidizing reaction(s), so that the number of electrons transferred to the total oxidizing agent component will be the same as when the above-stated amounts of hydrogen peroxide are used as the only oxidizing agent. (Hydrogen peroxide is expected to transfer two electrons per mole according to the half-reaction equation 2H++2exe2x88x92+H2O2xe2x86x922H2O.)
(Some uses of the nickel salt solutions prepared could be damaged by the presence of residual peroxide in a solution made as described above when a molar excess of hydrogen peroxide over nickel is used. As is known to those skilled in the art, even a small excess of hydrogen peroxide can be conveniently detected by a starch-iodide test solution. If peroxide is found by this test in a sample of the prefiltered nickel salt solution made by a process according to this invention, it is recommended that the amount of residual peroxide be analytically determined and a sufficient amount of nickel powder to consume this peroxide be added to the solution before filtration.)
When a precursor aqueous acidic liquid with its sole or predominant (i.e., at least, with increasing preference in the order given, 60, 70, 80, 90, 95, or 99% of its) acid content consisting of one or more oxyphosphorus acids is reacted with a nickeliferous solid in a process according to this invention, the concentration of the acid, measured as its stoichiometric equivalent as orthophosphoric acid, in the precursor aqueous acidic liquid at the beginning of reaction preferably is at least, with increasing preference in the order given, 10, 20, 25, 30, 35, 38, or 41% and independently preferably is not more than, with increasing preference in the order given, 75, 65, 55, or 45%. The minimum concentration preference is to avoid uneconomically long reaction times, while the maximum concentration preference is to avoid at least one of excessive viscosity, inadequate solubility of the nickel salts formed in the acid solution, and any danger of explosion as a result of rapid generation of hydrogen. Furthermore and independently, the ratio of the mass of oxyphosphorus acid molecules, measured as their stoichiometric equivalent as orthophosphoric acid molecules, preferably has a ratio to the mass of nickel in the nickeliferous solid reacted with the oxyphosphorus acid molecules that is at least, with increasing preference in the order given, 1.0:1.00, 2.0:1.00, 3.0:1.00, 3.5:1.00, 4.0:1.00, 4.3:1.00, or 4.6:1.00 and independently preferably is not more than, with increasing preference in the order given, 10:1.00, 8:1.00, 7.0:1.00, 6.5:1.00, 6.0:1.00, 5.6:1.00, 5.2:1.00, or 4.8:1.00. The reasons for these preferences are substantially the same as for the analogous concentration preferences noted last above.
When a precursor aqueous acidic liquid with its sole or predominant (i.e., at least, with increasing preference in the order given, 60, 70, 80, 90, 95, or 99% of its) acid content consisting of hydrofluoric acid is reacted with a nickeliferous solid in a process according to this invention, the concentration of the acid in the precursor aqueous acidic liquid at the beginning of reaction preferably is at least, with increasing preference in the order given, 1.0; 3.0, 5.0, 6.0, 7.2, 7.4, or 7.6% and independently preferably is not more than, with increasing preference in the order given, 70, 60, 50, 40, 30, 20, 15, or 10%. The minimum concentration preference is to avoid uneconomically long reaction times, while the maximum concentration preference is to avoid at least one of excessive viscosity, inadequate solubility of the nickel salts formed in the acid solution, and any danger of explosion as a result of rapid generation of hydrogen. Furthermore and independently, the ratio of the mass of hydrofluoric acid molecules in the precursor aqueous acidic liquid preferably has a ratio to the mass of nickel in the nickeliferous solid reacted with the precursor aqueous acidic liquid that is at least, with increasing preference in the order given, 0.30:1.00, 0.50:1.00, 0.60:1.00, 0.70:1.00, 0.80:1.00, 0.90:1.00, or 1.00:1.00 and independently preferably is not more than, with increasing preference in the order given, 10:1.00, 5:1.00, 3.0:1.00, 2.0:1.00, 1.8:1.00, 1.6:1.00, 1.4:1.00, or 1.2:1.00. The reasons for these preferences are substantially the same as for the analogous concentration preferences noted last above.
The reaction between solid nickel and aqueous acidic liquid to form nickel salts that become dissolved in the aqueous acidic liquid normally generates hydrogen gas, most of which escapes from the liquid. When little or no oxidizing agent is present in the aqueous acidic liquid, the generation of hydrogen in a process according to the invention has been observed to be stoichiometrically equivalent to the amount of nickel dissolved according to the chemical reaction: Ni+2H+xe2x86x92Ni+2+H2. When the relative amounts of oxidizing agent preferred for dissolving large pieces of nickeliferous solid are present in the aqueous acidic liquid used in a process according to the invention, the amount of evolved hydrogen sometimes is substantially less than a stoichiometric amount according to the simple reaction equation above, but some gas almost always has been observed to be evolved even in the presence of large relative amounts of oxidizing agent. Hydrogen gas is, of course, flammable and potentially explosive when mixed with air, so that proper safety precautions, which will be known to those skilled in the art, should be taken against any corresponding hazard in a process according to the invention.
A xe2x80x9cbatchwisexe2x80x9d process according to the invention is defined as one in which a single volume of aqueous acidic liquid is reacted with a specified volume of nickeliferous solid. The specified volume of solid can be mixed with the single volume of liquid either all at once at the beginning of the process, or the volume of solid can be divided into portions that are added one by one to the single volume of liquid, waiting until most of one portion of solid has dissolved before adding any additional portion of the solid. A batchwise process according to the invention is generally preferred for convenience on even a moderately large scale, up to at least a few thousand kilograms of nickel salt containing solution to be manufactured, although on a still larger scale a continuous process in which aqueous acidic liquid and nickeliferous solid are continuously input and product aqueous acidic solution of nickel salts is continuously output will become preferred.
The temperature at which a batchwise process according to the invention is performed preferably varies, most preferably monotonically, from an initial value that is at least, with increasing preference in the order given, 15, 20, or 22xc2x0 C. and independently preferably is not more than, with increasing preference in the order given, 31, 29, or 27xc2x0 C. to a final value that is at least, with increasing preference in the order given, 65, 68, 71, 74, or 76xc2x0 C. and independently preferably is not more than, with increasing preference in the order given, 95, 90, 85, 80, or 77xc2x0 C. If the temperature is too low, a very long reaction time will be required, while if the temperature is too high, foaming of the reaction mixture and related practical difficulties associated with generation of large volumes of gas in a short time are likely. As normally expected from general physical chemistry principles, at a constant temperature, the reaction rate in a process according to the invention is usually greatest when the aqueous acidic liquid reacted contains little or no dissolved nickel salts and decreases with increasing accumulation of nickel salts in the liquid, while at constant concentration of dissolved nickel salts and acid, the reaction rate increases with increasing temperature. It has accordingly been found necessary, in order to achieve an at least approximately optimal reaction rate throughout an entire batchwise process according to the invention, to raise the temperature as the aqueous acidic liquid becomes more concentrated in dissolved nickel cations. More particularly, when temperature control of the aqueous acidic liquid reacted is available as preferred, the temperature is, in one particularly preferred embodiment of the invention, raised from the initial value in increments that are at least, with increasing preference in the order given, 1.0, 1.5, 2.0, or 2.5xc2x0 C. and independently preferably are not more than, with increasing preference in the order given, 25, 20, 15, 10, 7, 5, 4.5, 4.0, 3.5, or 3.0xc2x0 C. and after the temperature target for each incremental increase has been attained, the temperature is not raised again by external heating for a time that is at least, with increasing preference in the order given, 2, 5, 8, 11, or 14 minutes and independently preferably, unless the temperature is at least 55xc2x0 C., is not more than, with increasing preference in the order given, 55, 45, 35, 25, 20, or 16 minutes. After the aqueous acidic liquid has reached the final intended temperature, this temperature is preferably maintained for a time that is at least, with increasing preference in the order given, 1.0, 2.0, 3.0, 4.0, 5.0, or 5.9 hours and independently preferably is not more than, with increasing preference in the order given, 24, 20, 16, 12, 10, 8, or 6.1 hours. If oxidizing agent is desired and has not been previously added, it then is preferably added to the mixture at its intended final temperature, which preferably is maintained for another time interval that is at least, with increasing preference in the order given, 15, 25, 35, 45, or 55 minutes and independently preferably is not more than, with increasing preference in the order given, 4.0, 3.0, 2.0, 1.5, or 1.1 hours. The solution is then preferably cooled to a temperature that is not more than, with increasing preference in the order given, 50, 45, 40, 35, or 30xc2x0 C. and independently preferably is not less than, with increasing preference in the order given, 20, 24, 27, or 29xc2x0 C. and then filtered through a filter that retains particles as much as, with increasing preference in the order given, 10, 8, 6, 4, 2.0, 1.5, 1.0, or 0.5 xcexcm in diameter. The solution is then ready for use.
In some of the uses of the nickel salt solutions prepared in a process according to this invention, the presence of even small quantities of some impurity elements can cause serious problems. It is therefore preferred that sufficiently pure reagents be used in a process according to the invention and introduction of contaminants be sufficiently well prevented that the product nickel salt solution will not contain more than, with increasing preference in the order given, 1000, 500, 200, 100, 50, 20, 18, 16, 14, 12, or 10 ppm of any of the following elements, the preference being independent for each element: Ag, Ti, Zr, Sn, Ca, Al, Mo, Sr, La, Ba, Si, Mn, Fe, Cr, Mg, V, Na, Be, B, Cu, Pb, Li, K, Rb, Cs, Fr, Ra, Sc, Cd, Zn, Ga, As, Se, Br, I, Te, Sb, In, Pd, Rh, Ru, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, TI, Bi, Po, Ac, Th, Pa, U, Np, Am, Cm, Bk, and Cf.
The invention may be further appreciated from the following examples and comparison examples.